You can calculate energy usage to determine product's efficiency

Q: Whenever I shop for an electric or gas appliance, I hear and see many efficiency claims. Determining which are legitimate gets confusing. How can I compare the

Q: Whenever I shop for an electric or gas appliance, I hear and see many efficiency claims. Determining which are legitimate gets confusing. How can I compare the

products?

A: Depending on the type of product and the fuel it uses, efficiency ratings can mean different things. Also, some manufacturers or salespeople play fast and loose with the accuracy of efficiency claims.

A basic definition of efficiency for any energy-consuming product is the amount of usable energy (heat, light, sound, etc.) output divided by the energy input.

The

energy input is usually an electric plug in the wall or a gas or propane line into the house. Electricity input is usually measured as wattage, and gas or propane input as British thermal units (or Btu) per hour.

For nonenergy-consuming products, efficiency is more difficult to compare. Home products such as doors, windows and skylights base the efficiency rating on an industry testing standard. Keep in mind, the conditions at your house might be different from the test standard, so also seek the advice of reputable contractors.

For windows and doors, the efficiency is related to how airtight they are and what the U-value (heat-flow characteristic) is when tested to the industry standard. Always ask who tested the product. It should be an independent laboratory or an industrywide trade association. Check with Energy Star (www.energystar. gov) for listings of the most efficient models.

Most plug-in electric heating devices and heaters, from the cheapest models to those that cost $400, are almost 100 percent efficient. All of the electricity consumed ends up as heat in the house. The differences in operating costs depend on how the devices are used and whether the design is proper for your needs.

Always read efficiency claims thoroughly when comparing products. For example, some lower-quality gas space heaters might claim a high 90 percent combustion efficiency, which refers to how efficiently the gas burns, not how efficiently the heat is transferred into your house. Its actual heating efficiency might be only 70 percent.

For electrical appliances such as window air conditioners, calculate the efficiency by dividing the Btu-per-hour cooling output by the electric wattage shown on the nameplate.

For other major appliances such as washers and refrigerators, rely on the yellow energy label.

Your usage habits often have more effect on the efficiency than the appliance's design.

For central heating and cooling equipment (furnaces, air conditioners and heat pumps), the manufacturer's efficiency ratings should be accurate.

Q: I have a large microwave oven that has a glass turntable in it. I have heard I should not remove the turntable, but I want to put a large rectangular casserole in there. Can I remove the turntable?

A: The purpose of a turntable in a microwave oven is to rotate the food for more even cooking. Many smaller and older microwave ovens don't have a turntable.

The only problem you might have is that the hub, which sits in the bottom of the turntable, will still turn. This will rub on the bottom of the casserole. Use plastic spacers, not metal, to raise the casserole a little.